Abstract
In this study a measurement technique for determination of equivalence ratio fluctuations from flame chemiluminescence in a kerosene-fuelled lean premixed combustor under atmospheric conditions is presented. Firstly, fundamental investigations into the relationship between the ratio of different chemiluminescence signals and the equivalence ratio are carried out using an imaging spectrometer. The chemiluminescence intensity is recorded for a wide range of equivalence ratios and fuel mass flows during steady state operation. The spectra show that the CH*/OH* ratio depends linearly on the equivalence ratio and is independent of the mass flow in the investigated range. Moreover, the background radiation has no influence on the monotonous trend of the CH*/OH* ratio for kerosene combustion. This interesting finding opens up new possibilities for passive optical measurement of the equivalence ratio in kerosene flames. Bandpass-filtered phase-correlated images of OH* and CH* chemiluminescence of an acoustically excited flame are taken simultaneously on one camera chip using an image doubler. After distortion correction, the image pair is used to calculate the global equivalence ratio from the CH*/OH* ratio. Based on the calibration chart derived in stationary operation, phase-resolved equivalence ratio perturbations are determined during acoustic excitation. The presented technique allows a quantitative measurement of equivalence ratio fluctuations in spray combustion and can therefore provide a better understanding of the fundamental mechanisms of thermoacoustic instabilities triggered by equivalence ratio fluctuations.Graphic abstract
Highlights
Modern gas turbine engines used in power generation are mainly operated at lean premixed combustion conditions to comply with current regulatory requirements (Candel et al 2013)
The change from diffusion combustion to premixed combustion has led to a significant reduction in nitrogen oxide emissions. These low-pollution combustors are prone to the formation of thermoacoustic instabilities causing significant pressure and temperature amplitudes in the combustion chamber (Lieuwen and Yang 2005; Huang and Yang 2009). These are caused by a feedback loop between acoustic waves in the combustion chamber and fluctuations in the heat release rate
Investigations of lean premixed gas turbine combustion dynamics have revealed that the heat release fluctuations can be attributed to two coupling mechanisms (Ducruix et al 2003; Lieuwen et al 2001)
Summary
Modern gas turbine engines used in power generation are mainly operated at lean premixed combustion conditions to comply with current regulatory requirements (Candel et al 2013). These low-pollution combustors are prone to the formation of thermoacoustic instabilities causing significant pressure and temperature amplitudes in the combustion chamber (Lieuwen and Yang 2005; Huang and Yang 2009). These are caused by a feedback loop between acoustic waves in the combustion chamber and fluctuations in the heat release rate. Investigations of lean premixed gas turbine combustion dynamics have revealed that the heat release fluctuations can be attributed to two coupling mechanisms (Ducruix et al 2003; Lieuwen et al 2001).
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